This invention relates to ultrasonic diagnostic imaging systems and, in particular, to a method and apparatus for editing and trimming individual frames from which an extended field of view ultrasonic image is composed.
Significant effort has been devoted to extending the field of view of ultrasound images so that a larger area of tissues and organs could be viewed in a single image. Early extended field of view (xe2x80x9cEFOVxe2x80x9d) imaging systems, known as xe2x80x9cB-arm scanning systems,xe2x80x9d included a single beam ultrasound transducer mounted at the end of an articulated arm. The joints of the articulated arm contained sensors that produced an electrical signal indicative of the spatial position of the transducer. As the transducer was scanned over the body of the patient, a scan line was produced from the ultrasound returns obtained from the transducer and the relative spatial locations of the transducer while the returns were being obtained. The scan lines from multiple adjacent scans of the transducer were computed and stored, and then assembled in consecutive, side-by-side locations to create an EFOV or xe2x80x9cpanoramicxe2x80x9d image. These early EFOV systems were thus capable of generating an ultrasonic image that could laterally extend for the maximum number of successive scan lines that the system could store and display and over the range of positions that arm could extend.
In recent years electronically scanned array transducers have been adapted for the same purpose. Since an electronically scanned array transducer automatically produces a two dimensional image, movement of the array transducer in the plane of the image will produce successive, spatially offset two dimensional images. Each new image or xe2x80x9cimage framexe2x80x9d in a new spatial location can be spatially registered with a previously acquired image frame that it overlaps, then combined with the previous image frames to produce an EFOV or panoramic image that is laterally extensive in the direction of motion of the array transducer. In some commercially available panoramic imaging systems, more than 80-90 percent of each image frame overlaps an adjacent image frame. The extent of the panoramic image is determined by the capacity of the ultrasound system to store and display multiple partially overlapping two dimensional images.
Prior art panoramic imaging systems are capable of producing a continuous panoramic image as a scanhead is continually moved in a given direction along the surface of the body. In such systems, the EFOV or panoramic image is generated in real time from image frames as the image frames are being acquired. However, a clinician acquiring a panoramic image in this manner is often trying to image a structure of extended length in the body, such as a blood vessel in an arm or leg. Although the clinician is trying to maintain the vessel in alignment with the image plane of the scanhead, frequently the path of the vessel and the moving scanhead will move out of alignment and the vessel will no longer appear in the image. In such circumstances, the usual recourse is to repeat the scan from the beginning, thereby unduly extending the time required to acquire the panoramic image. To solve this problem, a system described in U.S. patent application Ser. No. 09/345,242 to Roy B. Peterson et al. entitled xe2x80x9cEXTENDED FIELD OF VIEW ULTRASONIC IMAGING DIAGNOSTIC IMAGING WITH IMAGE REACQUISITION,xe2x80x9d which is incorporated herein by reference, allows the clinician to compensate for the premature termination of the scan by being able to reacquire the blood vessel in the EFOV image. In operation, newly acquired image frames may be obtained for an EFOV image by moving the scanhead in either direction. Thus, if the scanhead moves such that structure of interest is out of the scan plane of the EFOV image, the clinician may reverse the direction of the scan until the structure is reacquired in a new image frame, preferably at the point at which it initially disappeared from view. The resulting panoramic image is then composed of the original image frames and the repeated image frames. The clinician can therefore recover from misalignment of the structure of interest and the scan plane and continue the scan without having to restart the scan from the beginning.
Although the system described in the above-identified application to Peterson et al. is primarily designed to reacquire a vessel or tissue of interest, it can also be used to repeat image frames that contain defects that would impair the usefulness of the resulting panoramic image. For example, the clinician may inadvertently lift the scanhead from the skin during a scan, particularly at or toward the end of the scan. Lifting the scanhead in this manner causes phenomena known as xe2x80x9cflash artifactxe2x80x9d in which all or a portion of the image frame is seriously blurred. Flash artifact may also be caused by other defects in individual frames. If an image frame exhibiting flash or any other image artifact is combined with other image frames to produce a panoramic image, the panoramic image may be seriously degraded in the area in which the image frame exhibiting flash artifact was used.
Although the above-described system allows defects in an image to be corrected without repeating the entire scan, the defects must be noticed and corrected in real time as the image is being obtained. If the defect is not noticed until the entire panoramic image has been obtained, the entire scan must be repeated to obtain an entirely new panoramic image. Furthermore, since the panoramic image is created by the image frames as the image frames are being obtained, it is not possible to improve or enhance the panoramic image by subsequently processing or eliminating individual image frames.
There is therefore a need for a system and method for allowing image frames to be individually examined during or after the image frames making up a panoramic image have been obtained so that the individual image frames can be eliminated from the image frames that have been combined to produce the panoramic image.
A panoramic ultrasound imaging system and method in accordance with the invention acquires ultrasound image frames in a conventional manner. However, instead of simply combining the image frames to produce a panoramic image, data corresponding to the individual image frames are saved in a frame memory, and the data are retained after the image frames have been combined to create the panoramic image. As a result, defects in the panoramic image created by flash and other artifacts in an individual image frame can be removed by simply re-creating the panoramic image from all of the stored image frames except the image frames exhibiting artifacts. In addition to editing the panoramic image in this manner, the panoramic image can be trimmed at either end by eliminating portions of individual image frames extending beyond a specific line. The individual image frames my be examined for artifacts either manually or automatically using predetermined criteria, and they may be examined to edit the panoramic image either after all of the image frames have been combined to create the panoramic image or in real time as the image frames are being obtained.